runtime: add runtime.Hexdump protected by -tags=runtime_hexdump

src/runtime/hd.go

@@ -0,0 +1,112 @@
+//go:build runtime_hexdump
+
+package runtime
+
+import "unsafe"
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+
+	return b
+}
+
+func Hexdump(p []byte) {
+	var hd hexdumper
+	var completedBytes int
+	for i := 0; i < len(p); i += 16 {
+		m := min(len(p), i+16)
+		hd.format(p[i:m])
+		completedBytes += m - i
+		hd.offset += uint(m - i)
+	}
+}
+
+var hex = []byte("0123456789abcdef")
+
+type hexdumper struct {
+	offset uint
+	line   [83]byte
+}
+
+func (hd *hexdumper) format(buf []byte) {
+	// addr:_(hex dump)+spaces+space+bar+chars+bar+newline
+	line := hd.line[:]
+	ptr := 0
+
+	offs := hd.offset
+	ptr += 8
+
+	line[ptr] = ':'
+	ptr--
+
+	for offs > 0 {
+		line[ptr] = hex[offs&0x0f]
+		ptr--
+		offs >>= 4
+	}
+
+	for ptr >= 0 {
+		line[ptr] = '0'
+		ptr--
+	}
+
+	ptr = 9
+	line[ptr] = ' '
+	ptr++
+
+	for i, b := range buf {
+		if i%4 == 0 {
+			line[ptr] = ' '
+			ptr++
+		}
+
+		line[ptr] = hex[b>>4]
+		ptr++
+		line[ptr] = hex[b&0x0f]
+		ptr++
+		line[ptr] = ' '
+		ptr++
+
+	}
+
+	// fill in rest of line
+	for i := len(buf); i < 16; i++ {
+		if i%4 == 0 {
+			line[ptr] = ' '
+			ptr++
+		}
+
+		line[ptr] = ' '
+		ptr++
+		line[ptr] = ' '
+		ptr++
+		line[ptr] = ' '
+		ptr++
+	}
+
+	line[ptr] = ' '
+	ptr++
+	line[ptr] = ' '
+	ptr++
+	line[ptr] = '|'
+	ptr++
+
+	for _, v := range buf {
+		if v > 32 && v < 127 {
+			line[ptr] = v
+		} else {
+			line[ptr] = '.'
+		}
+		ptr++
+	}
+
+	line[ptr] = '|'
+	ptr++
+
+	line[ptr] = '\n'
+	ptr++
+
+	print(unsafe.String(&line[0], ptr))
+}